When 18-year-old Jon Angle set his sights on a ＄5,000 motorcycle last month, he was determined not to let a little thing like lack of funds stand in his, way. 'My bank said they'd never loan me that sort of money, since I don't really have any assets yet,' the recent high school graduate from Littleton, Colo., recalls. Still, Angle was able to secure a loan from the Young Americans Bank in Denver, which caters to the under-22-year-old crowd and permits allowance to be listed as a source of income on loan application. Now, with a new Suzuki, Angle is setting aside most of the income from his ＄6.75-an-hour job at a local McDonald's to pay off his debt. At mails, movie theaters and even motorcycle dealerships around the country, teenagers like Jon Angle are behaving like the fiscal equivalent of the Energizer Bunny: They keep spending, and spending, and spending. Last year, 12-to-19-year-olds went on their biggest shopping spree ever, ringing up ＄109 billion in purchases, a 38 percent increase over 1990. And the demographics for the teen market are enough to make any orthodontist smile. As the baby boomers' babies hit puberty, the teen population is expected to balloon from 29.1 million to 34.9 million by 2010. Teens also are earning money. About half of all 16-to-19-year-olds have part-time jobs, according to Teenage Research Unlimited, a market research firm. Combined with allowance from their parents, adolescents average ＄64 in income per week. But that money bums a quick hole in their pockets. For every dollar teens earned last year, they spent 84 cents. And even when they do put aside some of their funds, teenagers save only until they can afford some coveted big-ticket item. Clair Boetticher, 17, from North Dallas, Texas, for example, receives ＄35 in weekly allowance and is earning an extra ＄100 a week this summer working on a ranch. She spends most of money on food, movies and compact disks. And when Boetticher does save, she usually hangs onto the money only enough to buy tickets to a rock concert. With all this money up for grabs, it is no longer just makers of acne medication who are zeroing in on adolescents. Nike, for example, which consistently ranks as one of the most popular brands among teens, targets its products to consumers between the ages of 14 and 24. And Levi Strauss consults a panel of several hundred teens around the country during its product-development process. If the feedback indicates that the cut on a pair of jeans needs changing, the designers return to the drawing board. Teens don't just spend their money, they also affect the way their parents shop. When it comes time to buy a family computer, for example, grown-ups often turn to their kids as technology consultants. With an increasing number of children using PCs at school, it's not surprising that parents who buy home computers let their teens influence the decision about two third of the time. What is the main idea of the passage?